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I am running a third party software on a W2008 server. This client connects to a server via TCP. The average ping times between the two are 1ms. However, when I check the tcp connection in resource monitor for the app it shows the latency as 20ms.

I ran packet capture on the client side interface and see the ack times <1ms. The tcp settings on the client side are as follows:

Receive-Side Scaling State          : enabled 
Chimney Offload State               : automatic 
NetDMA State                        : enabled 
Direct Cache Acess (DCA)            : disabled 
Receive Window Auto-Tuning Level    : normal 
Add-On Congestion Control Provider  : ctcp 
ECN Capability                      : disabled 
RFC 1323 Timestamps                 : disabled 

Also I have set the TcpNoDelay and TcpAckFrequency as 1 in the registry for the specific interface. The NIC has offload enabled.

How does the resource monitor calculate this 20 ms TCP latency? Are there any other TCP settings in Win2008 that might reduce this latency?

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Is the resource monitor Windows PerfMon, or in the app? If it's in the app, we'll need to know the app before we can answer how the app calculates latency. –  sysadmin1138 Feb 10 '11 at 18:42
    
Windows Perfmon –  user70303 Feb 10 '11 at 20:13
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1 Answer

So to start with, resource monitor/perfmon uses a different measurement system to what wireshark etc uses, so that would be why the latency is different.

Without going into the depths of windows API, the difference is caused by post-processing and low priority.

Given the actual latency is 1ms, no there aren't any further settings you could apply, and I'm not aware of any changes you could make to 'fix' the windows API perfmon so it displays the 'correct' latency.

If you like I can find the exact reason why perfmon is slower, but based on previous experiences aforementioned reason is why.

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